Description Drs. Rykiel, Wu, Folse, and Archer propose to build and test dynamic, spatially explicit models of vegetation interactions that permit a mechanistic basis for (1) understanding local spatial interactions among individual plants, (2) generating spatial processes in succession, and (3) studying how small scale processes can produce and regulate large scale patterns. They will use vegetation clusters as model ecosystems for developing theory and simulation models explicitly linking plant and landscape levels of organization. The theoretical component of the proposed research is based on the hypothesis that local (individual and neighborhood) behavior determines the ecological patterns observed at larger scales (community and landscape). The modeling component involves development of (a) object-oriented simulation models representing spatial interactions between individual plants in clusters, and between clusters in the landscape, and (b) simplified grid-based (cellular automata) models of spatial interactions in cluster development. Field data will be collected on leaf area, transpiration, growth rate, and root extent for savanna and thorn scrub vegetation for model parameterization and evaluation. They will use the theory, models, and field data to predict the effects of spatial heterogeneity in nutrient availability on the formation and growth of vegetation clusters, the dynamics of individual clusters, and the interactions among clusters that produce observed and expected landscape patterns of vegetation and resource distributions. Drs. Rykiel, Wu, Folse and Archer are leaders in the field of vegetation in cluster development. The facilities available for conducting this research are outstanding.